Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed operations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly, can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
The manufacturing of smaller semiconductor devices relies on implementing improvements to horizontal and vertical electrical interconnection between multiple semiconductor devices on multiple levels, i.e., three dimensional (3-D) device integration. One approach to achieving the objectives of greater integration and smaller semiconductor devices is to focus on 3-D packaging technologies including PoP. However, PoP often requires laser drilling to form interconnect structures, which increases equipment cost and requires drilling through an entire package thickness. Laser drilling increases cycle time and decreases manufacturing throughput. Vertical interconnections formed exclusively by a laser drilling process can result in reduced control for vertical interconnections. Unprotected contacts can also lead to increases in yield loss for interconnections formed with subsequent surface mount technology (SMT). Furthermore, conductive materials used for forming vertical interconnects within PoP, such as copper (Cu), can incidentally be transferred to semiconductor die during package formation, thereby contaminating the semiconductor die within the package.
The electrical interconnection between a PoP and external devices can be accomplished by forming redistribution layers (RDLs) within a build-up interconnect structure over both a front side and a backside of a semiconductor die within the PoP. However, the formation of multiple RDLs over both a front side and a backside of the semiconductor die can be a slow and costly approach for making electrical interconnection between stacked semiconductor devices and can result in higher fabrication costs. The electrical interconnection between a Fo-PoP and external devices can also be accomplished by disposing an interposer over the Fo-PoP. However, using an interposer for electrical interconnection between semiconductor devices results in a thicker overall semiconductor package. In addition, as fabrication technologies improve, the number of input/output (I/O) pins per semiconductor device is increasing while the average semiconductor device size in pitch between adjacent interconnect structures is decreasing. Mounting semiconductor devices with increased I/O density to conventional motherboards can prove difficult because interconnection pads on conventional motherboards are typically configured with a larger pitch.